Functionally Graded Reinforced Concrete Beams under Mono-tonic Loading: A Review of Structural Performance and Failure Behavior

Functionally Graded Reinforced Concrete (FGRC) has emerged as a beneficial and sustainable construction method aimed at optimizing material efficiency and reducing the environmental impact of modern structures. Unlike con-ventional reinforced concrete (RC) structures, which require material uniformity, the FGRC approach strategically employs high-performance, enhanced concrete mixtures in zones subjected to high stress, while using standard con-crete in low-stress areas. This paper presents a comprehensive review of recent developments regarding the structur-al behavior, cracking patterns, and failure modes of FGRC beams subjected to monotonic loading. The findings indi-cate that appropriate functional grading in reinforced concrete beams delays initial crack formation, significantly enhances post-cracking stiffness, and improves overall load-bearing and energy-absorption capacities compared to conventional RC beams. Furthermore, incorporating engineered cementitious composites or fibers within the tension zones induces a pseudo-ductile response that effectively mitigates shear-induced tensile cracking. However, the structural reliability of FGRC beams remains heavily dependent on interlayer bonding, as premature delamination between adjacent layers can compromise the beam's integral structural action. Finally, this literature review high-lights significant research gaps, emphasizing the absence of standardized design codes, the lack of large-scale labor-atory experiments, and the need for robust numerical models based on the finite element method (such as ABAQUS) capable of accurately calculating long-term stress redistribution and complex failure limits in functionally graded reinforced concrete beams